Children with either normal or impaired cognitive abilities presenting to child and adolescent mental health services (CAMHS) with psychiatric or behavioural problems may have an underlying syndromic or neurological diagnosis. Diagnostic clues exist in the measurement of growth and head circumference, recognition of dysmorphism and in the full physical and, in particular, neurological examination of the individual. Recognition of these clues will allow referral, as necessary, for further investigation or surveillance. Prompt diagnosis of disorders is important for many reasons: the provision of an explanation for the child's current difficulties and the anticipation of further difficulties; the recognition of genetic, and therefore reproductive, implications for parents and siblings; the recognition of a grim prognosis; and access to any available treatments.